Intermittent left cervical vagal nerve stimulation damages the stellate ganglia and reduces the ventricular rate during sustained atrial fibrillation in ambulatory dogs

Background The effects of intermittent open-loop vagal nerve stimulation (VNS) on the ventricular rate (VR) during atrial fibrillation (AF) remain unclear. Objective The purpose of this study was to test the hypothesis that VNS damages the stellate ganglion (SG) and improves VR control during persistent AF. Methods We performed left cervical VNS in ambulatory dogs while recording the left SG nerve activity (SGNA) and vagal nerve activity. Tyrosine hydroxylase (TH) staining and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were used to assess neuronal cell death in the SG. Results We induced persistent AF by atrial pacing in 6 dogs, followed by intermittent VNS with short ON-time (14 seconds) and long OFF-time (66 seconds). The integrated SGNA and VR during AF were 4.84 mV·s (95% confidence interval [CI] 3.08–6.60 mV·s) and 142 beats/min (95% CI 116–168 beats/min), respectively. During AF, VNS reduced the integrated SGNA and VR, respectively, to 3.74 mV·s (95% CI 2.27–5.20 mV·s; P = .021) and 115 beats/min (95% CI 96–134 beats/min; P = .016) during 66-second OFF-time and to 4.07 mV·s (95% CI 2.42–5.72 mV·s; P = .037) and 114 beats/min (95% CI 83–146 beats/min; P = .039) during 3-minute OFF-time. VNS increased the frequencies of prolonged (>3 seconds) pauses during AF. TH staining showed large confluent areas of damage in the left SG, characterized by pyknotic nuclei, reduced TH staining, increased percentage of TH-negative ganglion cells, and positive TUNEL staining. Occasional TUNEL-positive ganglion cells were also observed in the right SG. Conclusion VNS damaged the SG, leading to reduced SGNA and better rate control during persistent AF.